The bottom line in furnace design is the HCCF, the “heat containment cost factor” it is defined as the cost per square meter to maintain a temperature of 1000°C inside the furnace and 106°C on the cold face. This works out at an F value of 100. To calculate it; the thickness of material required in cm = 100 x thermal conductivity in Watts/meter Kelvin. Multiply this by the density to get tons per square meter. Multiply this by the cost per ton to get the HCCF. This is the cost per square meter of furnace wall.

The table below shows that cellular insulation is up too 100 times more cost effective that the densest materials.

Cost Effectiveness:

To evaluate the cost effectiveness for cellular insulation materials, it is necessary to take into account several factors:

The Heat containment cost factor has been developed to this end. It is defined as the cost gradient of 1000°C on the hot face to 106°C on the cold face.

(F= 100)

The thickness of material required in cm is 100 x the thermal conductivity expressed in Waits per metre Kelvin.

This thickness is then multiplied by the density of the material to get the mass required per square metre.

The mass is then multiplied by the cost per kilogram.

This figure is the cost per square metre of the refractory to give the standard heat containment of 1000°C hot face to 106°C cold face. (TABLE 6)

Refractory lining are normally composed of layers of insulating material on the cold side and dense material on the hot side. TABLE 6 illustrates the importance of careful material selection. With good design, the size of a furnace can be greatly reduced, the thermal efficiency increased and the capital cost reduced.

TABLE 6: EXAMPLES OF HEAT CONTAINMENT COST FACTORS